#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
double xa,ya,xb,yb;
int main(void){
    while(~scanf("%lf%lf%lf%lf",&xa,&ya,&xb,&yb)){
        double ans=sqrt((xa-xb)*(xa-xb)+(ya-yb)*(ya-yb));
        printf("%.2lf\n",ans);
    }
    return 0;
}
